1. Field of the Invention
The present invention relates to an apparatus for mutual conversion between circular motion and reciprocal motion which is used for converting reciprocal motion of, e.g., the piston of a four-cycle reciprocating engine into rotary motion of a crankshaft.
2. Description of the Related Art
As one of the factors that hinder an increase in output efficiency of a four-cycle reciprocating engine, the unavoidable side thrust of a piston is known. This side thrust cannot be avoided since the piston and the crankshaft are coupled to each other by using a connecting rod. More specifically, since the reciprocal motion of the piston is not smoothly transmitted to the crankshaft, the side thrust is increased, thus causing an energy loss.
In this manner, conventionally, crank motion intervenes to convert linear motion into rotary motion. However, since the piston oscillates as the crank moves, in, e.g., a four-cycle reciprocating engine, a side thrust is generated between the piston and the cylinder. Therefore, the engine idling speed must be increased to about 1,000 rpm, causing a problem in fuel consumption as well.
The side thrust causes an energy loss. Moreover, the piston must be made of a heavy, strong metal in order to prevent damage to the piston, e.g., cracking, partial breaking, and the like of the piston caused by collision of the piston against the inner wall of the cylinder. Then, the weight of piston cannot be decreased by making the piston with, e.g., a ceramic.